A coverage area or cell in a cellular radiotelephone communication systems is provided by a Base Transceiver Station (BTS). The BTS communicates with the Mobile Subscribers (MS) via a defined air interface. In early cellular systems, each BTS communicated directly with a Mobile Switching Center (MSC). Later network architecture provided for each BTS to be connected and controlled by a Base Station Controller (BSC). The BSC and controlled BTSs form a Base Station System (BSS). A number of BSS's may be combined into a cellular radiotelephone communication system (FIG. 1) controlled by a MSC that, in turn, may be interconnected with a public switch telephone network (PSTN) composed of a number of trunk groups (N, Q, and P) (e.g. T1 lines).
The cellular system, covering a geographic area, allows MS's to communicate among MS's or a MS to communicate with a public switch telephone network (PSTN) subscriber through the PSTN interconnect provided at the MSC. Calls received through a BTS are routed to the BSC which, in turn, routes the call request to the MSC. The MSC then routes the call to a land party through the PSTN or to another MS back through a BSC and BTS.
The BSC provides message transfer and call switching as directed by the MSC. Control information received from an MS through a BTS of the BSC are routed to the MSC. Calls received by a BSC through the MSC, on a channel of communication link A, are switched under control of the BSC to the appropriate BTS in communication with the MS. Routing of all calls including those between MS's communicating through BTS's under the same BSC are routed through the MSC.
The MSC upon receipt of a call from an MS first determines whether the called party (target) is another MS under its control. If the target is another MS the MSC causes a page message to be generated for the target which is then transferred to each BSC which covers the location area in which the MS was last known to be in. The BSCs then cause the page to be transmitted through each antenna of each BTS connected to the BSC. Upon identification of a location of a target the MSC issues switching commands, directed to requesting and target BSCs, providing a signal path between the MS initiating the call and the BTS/BSC where the called party has been located.
If the MSC determines the target to be a PSTN subscriber, then the MSC composes a call request message to be transmitted into the proper trunk group of the PSTN interconnect. Trunk groups, in general and channels within trunk groups in particular, are associated with specific geographic areas. An MSC determines the geographic area in which the target is located by a translation of the called number and transmits the call request into the trunk group associated with the targers geographic area.
If the call request is received from the PSTN interconnect, then the MSC composes a page message for transmission through each BSS within the system. If the MS is within the system the MS responds through the nearest BTS. The response is transferred to the BSC, which in turn transfers the response to the MSC along with an identification of the receiving BTS. The MSC matches the call response with the call request and allocates a signal path from the PSTN interconnect to a selected trunk of the MSC to the BSC. The MSC instructs the BSC to connect the selected channel of the receiving BTS to the selected MSC trunk.
The BSCs is often located miles from the MSC, perhaps even in different PSTN area codes. Such remote locations can result in a landline telephone user having to pay toll call charges associated with having the voice "backhauled" to the MSC even when reaching a radiotelephone that is physically near the landline user. Similarly, a call from a radiotelephone to a nearby landline user may be routed miles to the MSC for connection to the PSTN and back to the landline user.
Spear (U.S. Pat. No. 5,036,531) provides one solution to this problem. The instant invention extends that solution by minimizing the charge impact on previously installed BSCs and "tricking" them into providing local PSTN interconnect functionality. The instant invention employs a control intercept to trick existing MSCs and BSCs into performing a similar function.